World Government (WG) is probably the largest organization in One Piece. It is made of number of organization. It represents alliance of all of the countries in Grand Line, except for Alabasta.
WG is ruled by 5 old men known as the Gorosei. They are considered to be most politically powerful men in the world.
The Marines of One Piece is a branch of WG. Marines being WG’s most powerful branch and main method of execution. They are all over the world and are feared by many. They are most famous for having the three admirals who are each one man army.
Impel Down is another branch, the greatest prison in the world. It holds the most powerful of criminals. Notable inmates include Crocodile, Ivankov, Buggy the Clown, and Portgas D. Ace. There was no one that ever escaped this place, until a certain pirate broke in and then out of this facility.
Cipher Pol (CP) is the secret intelligence/ spy agency of WG. CP is divided by numbers, ranging from CP0 – CP9. Only CP1 – CP8 are official. CP9, has license to kill and were main antagonists during the Water Seven arc and Enies Lobby arc. CP0 or Cipher Pol Aigis 0 are apparantly more powerful than CP9, but not much of them are known at this point.
And let’s not forget the Shichibukai AKA Seven Warlords of the Sea. I already did a World of article here. They are pirates that now work for WG, in return, they gain certain level of military rank as well as no longer being a wanted criminal.